.NET Framework 4.7.2中HttpApplication如何忽略JSON响应空属性

普通Web API（非OData）场景 #

直接在Global.asax.cs的Application_Start方法里配置JSON序列化规则：

var jsonFormatter = GlobalConfiguration.Configuration.Formatters.JsonFormatter;
jsonFormatter.SerializerSettings.NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore;

这段代码会让Web API返回JSON时自动跳过值为null的字段。

OData响应场景 #

OData有独立的序列化机制，需要自定义序列化器来实现：

1. 创建自定义的OData序列化器和提供器

public class CustomODataSerializerProvider : DefaultODataSerializerProvider
{
    public CustomODataSerializerProvider(IServiceProvider serviceProvider) : base(serviceProvider)
    {
    }

    public override ODataEdmTypeSerializer GetEdmTypeSerializer(IEdmTypeReference edmType)
    {
        var serializer = base.GetEdmTypeSerializer(edmType) as ODataResourceSerializer;
        if (serializer != null)
        {
            return new CustomODataResourceSerializer(this);
        }
        return base.GetEdmTypeSerializer(edmType);
    }
}

public class CustomODataResourceSerializer : ODataResourceSerializer
{
    public CustomODataResourceSerializer(ODataSerializerProvider serializerProvider) : base(serializerProvider)
    {
    }

    protected override void WriteStructuralProperty(ODataWriter writer, EntityPropertyMappingMapping epmMap, StructuralPropertySegment structuralProperty, IEdmStructuralProperty edmProperty, object propertyValue, ODataResourceContext resourceContext)
    {
        // 字段值为null时跳过写入
        if (propertyValue == null)
        {
            return;
        }
        base.WriteStructuralProperty(writer, epmMap, structuralProperty, edmProperty, propertyValue, resourceContext);
    }
}

2. 在Global.asax.cs的Application_Start里注册自定义提供器

GlobalConfiguration.Configuration.MapODataServiceRoute("ODataRoute", null, builder =>
{
    // 这里替换成你的OData实体配置，比如builder.EntitySet<Product>("Products");
    builder.SetSerializerProvider(new CustomODataSerializerProvider(GlobalConfiguration.Configuration.ServiceProvider));
});

这样OData响应里的null字段就不会被输出了。

内容的提问来源于stack exchange，提问作者Subhayan